114 Crown post offices will be closed for a 24-hour period, with no delivery or collection of cash from 11,500 sub-post offices across the UK.
Members of the Union of Communications Workers (CWU) are on strike over a wage freeze for 2021 and proposals for a 2 per cent increase from April this year along with a one-off payment of £ 250.
Trade union officials said the proposal was “extremely bad”, especially since RPI inflation reached 9 percent.
Employees of counters, as well as employees of the office, administration and call centers are involved in the dispute.
The CWU said all so-called crown post offices would be affected by the outlet, as well as smaller post offices.
The post office said the vast majority of its 11,500 branches were not affected by the strike and would operate normally.
Photographs posted on social media show workers on a picket line near closed post offices across the UK, including in Glasgow, Belfast, north London, Derbyshire and Durham.
CWU spokesman Andy Fury said: “Despite all the union’s attempts to avoid a strike, the post office has shown no interest in meaningful negotiations.
“So the workers gave a huge mandate to strike.
“The current proposal to increase wages by only 2 percent in two years is nothing more than an insult to these key workers who provided exemplary services to this country during the pandemic.
“As the cost of living crisis grows, working people across the country are facing harsh realities.
“This is no less true for postal workers, who deserve much better than the humiliating offer that now exists.
“The management of the post office should understand that by underestimating these workers, they have caused real anger across the country.
“We urge them to go to the table with us and reach a decent, fair agreement that shows respect for key UK workers who kept post offices open to the public during the pandemic.”
A post office spokesman said: “We want to assure our customers that this decision will not affect the vast majority of our 11,500 offices. [to strike] and will remain open throughout the day. ”
Additional Press Association reports